Relative clauses may be classified by three structural criteria:

  1. the type of subordination
  2. the position of the head in the complex sentence
  3. the position of an adnominal relative clause vis-à-vis the head.

This yields the following classification:

head position ╲

These kinds of relative clauses constitute types in the sense that each positional variant correlates with other structural properties of the construction.

An internal head relative clause contains that nominal expression which constitutes the semantic core of the complex concept to be formed. (In an alternative terminology, internal head relative clauses are called headless.) This nominal is in situ, i.e., it occupies that syntactic position inside the relative clause which it would occupy in an independent clause and which would be the relativized position in the external-head variety. Since it is neither an open clause nor overtly oriented towards one of its syntactic positions, it may look like a plain subordinate clause, unless the head is marked as such, as is the case in some internal-head varieties.

Adjoined relative clause

As to dependency relation, there are two main types of relative clauses, adjoined and embedded ones. An adjoined relative clause is an adjoined subordinate clause which embodies an anaphoric relation to a constituent of the main clause such that the subordinate clause may be interpreted as specifying the concept of that constituent.

An adjoined relative clause is not a constituent of the main clause and consequently not embedded in it, but rather adjoined at its periphery. Two positional varieties of the adjoined relative construction are known:

. yankiri-ḷikutja-lpaŋapaŋa-ṇu,ŋatjulu-ḷu∅-ṇapantu-ṇu
Walb [ emu-ERGSR-PROGwaterdrink-PST ]I-ERGAUX-SBJ.1spear-PST
The emu which was drinking water, I speared it.
/ While the emu was drinking water, I speared it.
(Hale 1976:78)
WalbI-ERGAUX-SBJ.1emuspear-PST[ SR-PROGwaterdrink-PST ]
I speared the emu which / while it was drinking water.(Hale 1976:78)

An adjoined relative clause may occupy a fixed position either preceding or following the main clause. By this distinction, it is either a preposed () or a postposed () relative clause. (These are not to be confused with the prenominal and the postnominal relative clauses, which are embedded beside their head nominal.) An adjoined relative clause which may shift between front and tail position of the complex sentence may be called shiftable.

Given the weak subordination of the relative clause, normal rules of anaphora apply to the construction. This means that in the default case, the head noun is part of the first clause of the bipartite construction, while the second clause resumes this antecedent anaphorically. Possible deviations from this default schema include the repetition of the head noun in both clauses. More on this in the section on anaphora.

The subordinate clauses of and are not explicitly oriented, which leads to the kind of ambiguity indicated by the alternate translations. The correlative diptych is a subtype of the adjoined relative construction in which at least the head function is explicitly marked.

Embedded relative clauses

The embedded relative clause is a constituent of its main clause. By their position vis-à-vis the head noun, three types of embedded relative clauses may be distinguished:

JapD1-TOP[ D3personwrite-PST ]bookCOP
This is the book that person wrote.(Andrews 1975:46)
.This is the book [ that person wrote ].
Dagbyouknow[ heSRgivestranger-SPEC.ANmoney ]PTL
You know the stranger he gave the money to.(Wilson 1963:141)

Prenominal and postnominal relative clauses are adnominal. The adnominal variety is most like an adjectival expanded to a clause. To the extent it is an adjectival, the combination with the head nominal is by attribution.

The adnominal relative construction functions as a nominal in the matrix clause. There, it will generally be determined in some way to form an NP. The nominal will be called higher nominal, in contrast with the head nominal.

The circumnominal variety is a nominalized clause in substantive function. It contains its head nominal in situ and is understood as specifying the latter's concept. From a semantic point of view, the proposition is oriented towards the position occupied by the head. However, this orientation may or may not be made explicit.

Other features relevant for the structural description of a relative clause include the means by which it is subordinated and nominalized/adjectivized, the means that links it as an attribute to the head nominal and the way the head is represented in the subordinate clause. This latter aspect is connected with the syntactic functions that the head may have inside the relative clause, which largely follow the accessibility hierarchy.